As the method for medicine administration into human or other living bodies, methods by oral administration or injection are known widely. As an administration method coming next to them, a method by transdermal administration is drawing attention. The transdermal administration method enables painless administration of a medicine to an intended affected part over a long period of time. Further, the transdermal patch used in the transdermal administration method has various advantages such as small size, easy carrying and the like. Hence, development of various transdermal patch has been made in recent years.
These transdermal patchs have a medicine layer wherein a medicine solution is impregnated into a medicine-holding material such as hydrophilic polymer, cotton cloth or the like. In using such a transdermal patch, the medicine layer is allowed to make tight contact with the skin of living body. Thereby, the medicine is infiltrated into the living body through the skin.
In this administration method, the concentration difference of medicine acts as a driving force and the medicine is infiltrated into the living body, in general. However, since the infiltration rate of ordinary medicine into living body surface (e.g. skin or mucous membrane) is small, there is a problem that it is impossible to administer a large amount of a medicine into a living body at once. In order to increase the efficiency of medicine administration, it is conducted to enhance the medicine concentration in the transdermal patch used. In this approach, however, it is necessary to impregnate a medicine (which is expensive) into a medicine layer in an amount more than required in administration; consequently, the amount of medicine exceeding the amount required in administration becomes useless. Further, the medicine is administered into the living body in a solution state; therefore, when the solubility of medicine is low, there is a problem that it is impossible to obtain the medicine solution in a required amount.
As the method for alleviating these drawbacks in the transdermal administration of ionic medicine, there is known an iontophoresis method which comprises infiltrating a medicine ion into a living body by electrophoresis. Further, in order to increase the amount of medicine to be administered, there are proposals on a new iontophoresis method which comprises infiltrating a medicine ion into a living body through an ion-exchange membrane placed on the surface of a living body (JP 1991-94771A, National Publication of International Patent Application No. 1991-504343, JP 1992-297277A, JP 2000-229128A). The ion-exchange membranes used in these proposals are commercial products using, as the base material, a woven cloth, which is used in salt manufacture or dialysis of food compounds.
In the iontophoresis, an apparatus of complicated structure provided with electrodes for voltage application and an electric source is needed in administration of a medicine. Accordingly, the iontophoresis using an ion-exchange membrane is inferior in portability and small size which are the important merits of transdermal administration method and, moreover, has a problem that the apparatus used therein is inevitably expensive.